The purpose of this investigation is to: 1) determine the acute effects of nicotine patch on MRI parameters; 2) establish whether the acute MRI responses to IV nicotine are influenced by the nicotine patch; 3) establish the minimum interval between subsequent IV injections of nicotine that does not cause attentuation of the MRI response; and 4) compare the MRI signal changes following nicotine patch plus mecamylamine to those of nicotine patch alone.